Among the dental diseases caused by dental caries, there are pulpitis and infected root canal. In case of a healthy tooth, a central cavity (root canal) runs in the longitudinal direction within the tooth, and the root canal opens a fine hole (apical foramen) at the tip of the tooth, which receives blood through this fine hole, and nourishes the nerve fiber (dental pulp). When affected by pulpitis, the patient, suffering from a great deal of pain, will visit a dentist. In case of an infected root canal with developed necrosis of the pulp, on the other hand, lesion may sometimes develop within the tissue surrounding the root apex (periapical tissue). In such cases, previous treatment often consisted extracting the diseased tooth. With the progress of dental techniques, however, the operative dentistry to preserve the tooth (diseased tooth) without extracting it has become more popular. At present the practice is to remove the inflamed dental pulp under local anasthesia (extirpation of the pulp), or in case of an infected root canal, to remove the infected dentin, then clean, disinfect and fill the hollowed root canal compact with a filling material (canal filling). Variations depending on the dentist will make the kind of the tooth (such as canine, molar tooth or the like), the size of the tooth that varies according to the age and sex of the patient, the individual dietetics (this is considerably variant), and the conditions and the stage of the diseased tooth, and will give the treatment to the interior of the root canal (endodontic therapy), and preserve the diseased tooth.
Hereinafter, the filling agent to be used in canal filling in the endodontic therapy will be explained somewhat in detail. The surfaces of the root canal after extirpation of the pulp and the infected root canal are not only smooth but have the remaining protein, and particularly in case of the infected root canal, there are various impurities such as microorganisms and pus, and the surface of the root canal itself, being infected by microorganisms, is softened (soft dentin) to form a lesion deeply infected by microorganisms. The operation to disinfect chemically the interior of the root canal, is carried out then the infected dentine is removed using a reamer, and at the same time, the shape of the root canal (preparation of root canal). The basic technique of the preparation of the root canal is to enlarge the root canal with a reamer, then scrape the wall with a needle-like file similar in shape with that of a reamer, (the kind of file being able to scrape the surface when drawn inward) to smooth the wall surface. The disinfection and preparation of the root canal are the operating techniques that require a high technique and a good deal of patience but are quite important to carry out successfully the canal filling that follows and to preserve the diseased tooth in a favorable condition. The root canal itself is curved in many cases, and varies being branched (collateral routes) or narrowed in the middle, and has an anatomical shape so complicated that there are no root canals alike. In the interior of the prepared root canal, filling is compactly placed. The condition of the canal filling, whether it has been done well or not, becomes a factor that exerts a good deal of influence over the therapeutical process subsequent thereto. There are various filling materials that are called root canal sealers and the technique of filling also vary. But there are requirements for the root canal sealer; that is it can be completely solidified within the root canal after filling, and the components of the root canal sealer do not disintegrate out from the apical foramen, and of course it can be easily handled by the operator in filling.